Reed switch having contacts plated with a thin silver layer

ABSTRACT

A sealed contact dry reed switch in which nickel-iron reed contacts are held in a glass envelope by seals and in which the surfaces of the reed contacts, including those portions under the seals, are covered with a thin layer of silver.

United States Patent Ratliff et al. Sept. 5, 1972 [54] REED SWITCH HAVING CONTACTS [56] References Cited PLATED WITH A THIN SILVER LAYER UNITED STATES PATENTS [721 Inventors: Truman Ram, Pataskala; Paul 3,497,655 2/1970 Riff ..200/166 0 William Rena, Columbus, both of 3,251,121 5/1966 Prival ..200/166 0 x Ohm 3,495,061 2/1970 Coffin et al. ..200/166 c 3 249 728 5/1966 Sasamoto et al. ..200/ 166 C [73] Ass1gnee. Bell Telephone Laboratorles, Incorporated, Murray Hm, Ni 2,469,878 5/1949 l-lannon et al ..200/166 C [22] Filed: Sept. 23, 1971 Primary Examiner-l-l. 0. Jones 1 pp No: 182,957 AztorneyR. J. Guenther et al.

[57] ABSTRACT [52] US. Cl. ..200/166 C, 29/630 C A sealed ontact dry reed switch in which nickel-iron [51] Int. Cl. ..H0lh 1/02 reed contacts are held in a glass envelope by seals and [58] Field of Search ..200/166 C; 29/630 C in which the surfaces of the reed contacts, including those portions under the seals, are covered with a thin layer of silver.

5 Claims, 3 Drawing Figures 3 '3 l I f 77 L 77777, 7 ,f/ l3 BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to dry reed contacts which are typically sealed in a glass envelope to form a miniature switch and pertains in particular to the composition of a layer of conducting material disposed on the surface of the reed contacts.

2. Description of the Prior Art Miniature switches for controlling high frequency signals must exhibit low insertion loss when used in high frequency circuit applications. Where the switches comprise reed contacts encapsulated in a glass envelope, the seals between the reed contacts and the glass must be strong and reliable. Heretofore, low insertion loss has been achieved by plating the reed contacts with a noble metal such as silver. It has been difficult, however, to obtain suitable seal strengths.

Accordingly, one object of this invention is to achieve strong and reliable seals in reed switches adapted for high frequency use.

SUMMARY OF THE INVENTION In a preferred embodiment of this invention, a pair of nickel-iron reed contacts disposed in overlapping relationship with each other inside a glass envelope are each held in place by a seal so as to form a miniature switch and the surfaces of each reed contact, including that portion beneath the seal, is covered with a thin layer of silver to improve the strength of the seal and to provide low insertion loss characteristics when the switch is used in a circuit carrying high frequency signals. 7

According to one feature of this invention, improved seal strength, as well as low insertion loss, is achieved by plating the reed contacts with a layer of silver having a thickness in the range of 60 to 175 microinches.

DESCRIPTION OF THE DRAWING FIG. 1 is a side elevation view, taken in section, of a sealed contact dry reed switch made in accordance with this invention;

FIG. 2 is an end elevation, taken in section along the lines 22, of the sealed contact dry reed switch illustrated in FIG. 1; and

FIG. 3 is an end elevation, taken in section along the lines 3-3, of the sealed contact dry reed switch illustrated in FIG. 1.

DETAILED DESCRIPTION Referring to FIG. 1, a sealed contact dry reed switch is disclosed which includes an encapsulating envelope 11 and a pair of overlapping reed contacts 12. The envelope 11 is typically made of glass, while the reed contacts 12 are made of a nickel-iron composition such as 52 alloy. Each reed contact 12 is firmly joined to the vessel 1 1 by a seal 13 which is formed by melting the material of the envelope 11 until it adheres to the surfaces of the reed contacts 12.

As best understood from FIGS. 1 and 2, the entire surface of each reed contact 12 is covered by a silver layer 14. As shown in FIG. 3, each reed contact 12 is se ar tedf omits sea 13b th silver la r14.

?\s is well known, ii the i eed contacts I2 are coated by a silver layer 14, low insertion loss will be achieved when the reed switch 10 is used in a high frequency application, i.e., frequencies up to I00 megahertz. As can be seen from the following table, however, seal strengths drastically increase if the thickness of the silver layer 14 is limited to a range of- 60 to I microinches. When deposition conditions can be regulated closely, better results will be obtained by limiting the silver layer 14 to a thickness in the range of to I50 microinches. Best results, however, will be achieved by limiting the thickness to microinches.

While mating or contacting surfaces covered with silver can be used to make and break electrical circuits, other contact materials are preferable. Consequently, as shown in FIGS. 1 and 2, the overlapping portions of the reed contacts 12 are electrochemically stripped or otherwise treated until the silver layer 14 is removed. With the underlying nickel-iron alloy exposed, other contact materials such as a silver-gold alloy can be disposed thereon to serve as a contact surface.

Insummary, a sealed contact dry reed switch has been disclosed which is suitable for use in high frequency circuit applications and which exhibits high seal strengths. While only a single embodiment has been disclosed, it is illustrative of the principles of this invention and others skilled in the art will readily conceive of others which will fall within the scope of the invention.

What is claimed is:

l. A switching device including a pair of elongated nickel-iron contacts disposed with their tips in overlapping relationship and a glass envelope hermetically encapsulating the overlapping portions of said reed contacts and joined to each of said reed contacts by a glass-to-metal seal CHARACTERIZED IN THAT the surface of each reed contact, including that portion located beneath a seal, is covered by a thin layer of silver.

2. A switching device in accordance with claim 1 wherein the thickness of said layer of silver lies within the range of 60 to 175 microinches.

3. A switching device in accordance with claim 2 wherein a contacting portion located on one reed contact in registration with the corresponding contact portion on the other reed contact is devoid of a silver layer.

4. A switching device'in accordance with claim 1 wherein the thickness of said layer of silver lies within the range of 100 to microinches.

5. A switching device in accordance with claim 1 wherein the thickness of said layer of silver is 120 microinches.

UNITED STATES PATENT ()FFICE CERTIFICATE OF CORRECTION Patent No. 3 689 722 Dated g t b 5 912 lnv nt fls) Earl Truman Ratliff Piu Willia 3:13.1 1;

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 19 delete "silver." and substitute therefor --gold-s ilver alloy such as disclosed in the article beginning at page 203,

in Volume 48 of the Bell Laboratories Record.-.

Signed and sealed this 23rd day of January 1973.

(SEAL) Attest: v

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK I Attesting Officer Commissioner of Patents FORM PC4050 (10-69) USCOMM-DC 0 75 a urs GOVERNMENT rnmnun orncz: I959 0-366-3.H 

2. A switching device in accordance with claim 1 wherein the thickness of said layer of silver lies within the range of 60 to 175 microinches.
 3. A switching device in accordance with claim 2 wherein a contacting portion located on one reed contact in registration with the corresponding contact portion on the other reed contact is devoid of a silver layer.
 4. A switching device in accordance with claim 1 wherein the thickness of said layer of silver lies within the range of 100 to 150 microinches.
 5. A switching device in accordance with claim 1 wherein the thickness of said layer of silver is 120 microinches. 